1. Field of the Invention
The present invention relates to a light-emitting diode (LED) device, and more particularly to an LED device that has multiple LEDs and an active heat-dissipation device to dissipate the heat from the LEDs without depending on the ambient temperature and ventilation and even lowering the temperature of the LEDs under ambient temperature.
2. Description of the Related Art
Light-emitting diodes (LEDs) are power saving and are used generally for traffic signals, electric billboards, electric torches, desk lamps and projectors. However, LEDs with high power generate extreme heat when operating. Without a heat-dissipation device, the extreme heat from the operating LEDs may probably bum out the LEDs or greatly reduce their useful life.
In general, a core of an LED can bear a maximum temperature of 120° C., which is far lower than the temperatures that conventional bulbs can withstand. Therefore, the life of LEDs depends on the quality of a heat-dissipation device for the LEDs.
Furthermore, the intensity of an LED is relevant to the core temperature of the LED. Lowering the core temperature increases the intensity of the LED, as shown in the following Table 1.
TABLE 1Intensity increaseLED T1° C.Relative intensityfrom T1 = 90° C.9075Baseline6087+16%5091+21%4593+24%4095+27%25100+33%
Table 1 shows a relation of the core temperature (Tj) and the intensity of the LED. For instance, the life of an LED increases from 15,000 hours to 60,000 hours when a temperature of a base on which the LED is mounted is lowered from 85° C. to 55° C. and simultaneously the core temperature of the LED is lowered from 101° C. to 81° C.
Obviously, lowering the core temperature of the LED improves the life and intensity of the LED. Therefore, an LED device needs to be equipped with a heat-dissipation device to maintain the LED device at a low temperature to improve the life of the LED.
A conventional heat-dissipation device for an LED device has a heat sink and a fan. The heat sink is made of metal and is mounted to the LED device. The fan is mounted to the heat sink. However, the operating fan generates noise.
With reference to FIG. 4, an LED device has a hollow shade (93), a base (90), multiple LEDs (91) and a looped heat pipe (LHP) (92). The base (90) is mounted in the shade (93). The LEDs (91) are mounted to the base (90). The LHP (92) is mounted around the shade (93), is connected to the base (90) and has an axial channel and a liquid. The liquid exists in the axial channel and has a fine volatility. When the LEDs (91) operate and generate heat, the liquid in the LHP (92) absorbs the heat, flows along the LHP (92) and dissipates the heat through the whole LHP (92) and the shade (93). However, the heat-dissipation effect of the LHP (92) decreases when the size of the LED device becomes larger.
Moreover, both of the aforementioned heat sink and LHP provide a passive heat dissipation that depends on the difference between the ambient temperature and the temperature of the LEDs, and on the ambient ventilation. The seat sink and the LHP work ineffectively when the ambient temperature is close to the temperature of the LEDs or when ambient ventilation is bad.
To overcome the shortcomings, the present invention provides an LED device with an active heat-dissipation device to mitigate or obviate the aforementioned problems.